Three-dimensional printer

ABSTRACT

A three-dimensional printer uses inkjet-type printheads to rapidly prototype, or print, a three-dimensional model. A powder feeder includes a conveyor system and a metering system to deliver powder to a build area in measured quantities. The powder feeder also includes a vacuum system for loading powder into a feed reservoir or chamber. The vacuum system can also be used to cleanup excess powder. Other powder control features include powder gutters and magnetic powder plows. During printing, a cleaning system operates to remove powder from the printheads. In the event of a printhead or jet failure, the failure can be detected and corrective measures taken automatically. After printing, the model can be depowdered and infiltrated in an enclosure.

RELATED APPLICATIONS

[0001] This application is a Continuation-in-Part of U.S. applicationSer. No. 09/851,502, filed May 8, 2001, which is a Continuation-in-Partof U.S. application Ser. No. 09/416,787, filed Oct. 13, 1999, which is aContinuation-in-Part of U.S. application Ser. No. 08/771,009, filed Dec.20, 1996. This application also claims the benefit of U.S. ProvisionalApplication No. 60/325,310, filed Sep. 27, 2001. The entire teachings ofthe above applications are incorporated herein by reference in theirentirety.

BACKGROUND

[0002] Rapid prototyping describes various techniques for fabricating athree-dimensional prototype of an object from a computer model of theobject. One technique is three-dimensional printing whereby a specialprinter is used to fabricate the prototype from a plurality oftwo-dimensional layers. In particular, a digital representation of a 3-Dobject is stored in a computer memory. Computer software sections therepresentation of the object into a plurality of distinct 2-D layers. A3-D printer then fabricates a layer of material for each layer sectionedby the software. Together, the various fabricated layers form thedesired prototype.

[0003] An apparatus to build a three-dimensional part from powdertypically includes a powder supply and a build surface. Powder istransferred from the powder supply to the build surface in incrementallayers. In one method of three-dimensional printing, layers of a powdermaterial are deposited in a confined area. A binder solution isselectively deposited on each layer to produce regions of bound powder.A typical apparatus to deposit the binder is an inkjet-type printhead.The unbound powder is then removed to yield a three-dimensional part.

SUMMARY

[0004] The use of powder as a build material results in potentialproblems. Because the powder can easily become airborne, it canadversely affect the machinery, the final product, or human users. Thepowder can become airborne during various stages of the printingprocess: from loading the machine to cleanup. In addition, theaccumulation of excess powder, whether airborne or not, can lead tomaintenance problems within the printer. Prior 3-D printers have hadproblems controlling the powder.

[0005] In accordance with a particular aspect of the invention, anembodiment of a three-dimensional printer can include an apparatus thatcan comprise a feed reservoir, a vacuum system, a build chamber, and anoverflow cavity. The feed reservoir stores a supply of build materialfor forming the object. The build chamber receives incremental layers ofthe build material from the feed reservoir. The overflow cavity receivesan excess quantity of the build material transferred from the feedreservoir but not received by the build chamber.

[0006] The vacuum system can have its inlet plumbed to the feedreservoir. The vacuum system can then be used to transfer build materialinto the feed reservoir from various sources. More particularly, thevacuum system can be used to draw build material into the feed reservoirthrough a conduit attached to the inlet of the vacuum system.

[0007] For example, the vacuum system can be configured to fill the feedreservoir from a container of build material. This can further include adevice for injecting air into the container of build material. Thevacuum system can also be configured to remove loose powder from thebuild chamber after the object has been fabricated and to transfer theloose powder to the feed reservoir. The vacuum system can also beconfigured to empty the overflow cavity and transfer the build materialto the feed reservoir. The vacuum system can also be configured to cleanup powder deposited on or near the feed reservoir or the build chamberand return the cleaned-up powder to the feed reservoir. Any of the aboveexamples can be automated or done manually by the user.

[0008] The apparatus can also include a system for removing relativelylarge particles from the powder and returning the powder to the feedreservoir. That system can induce a cyclonic action to a flow stream ofpowder and air. The flow stream can pass through a separator screenbefore entering the feed reservoir.

[0009] The apparatus can also include a filter disposed within thevacuum system and a system to clean the filter. In the case of aplurality of filters, a cleaning system can then be used to clean thefilters. In particular, a reversed airflow can be delivered sequentiallythrough each of the filters. In that case, the cleaning system couldinclude valves to close the vacuum source to a single filter outlet andto then divert air at about atmospheric pressure into the same outlet,reversing flow direction and blowing off accumulated particles. Otherfilters in the system can be used to maintain airflow and vacuum insidethe vacuum chamber while one or more of the filters are being cleaned byreverse airflow.

[0010] Not only is it difficult to control the dissipation of thepowder, it can be difficult to transfer the powder from the powdersupply to the build area. First, the powder becomes compacted in thepowder supply and tends to clump into structures, such as bridges.Second, it can be difficult to deliver the powder in a smooth layer,which can lead to part defects. Finally, too much powder can betransferred, which leads to wastage and contributes to the buildup ofexcess powder and the amount of airborne powder.

[0011] In accordance with another particular aspect of the invention, anembodiment of a three-dimensional printer can include a chamber forstoring build material below the plane of the build surface and aconveyor. The conveyor can be coupled to the chamber and then be usedfor moving the build material. In addition, the conveyor can stir thebuild material within the chamber toward inhibiting the formation ofbridges of build material or stagnant areas.

[0012] More particularly, the conveyor can include a plurality of slatsattached to two strands of a conveyor chain, each slat dimensioned tocarry a quantity of build material. The slats can be shaped so as to bestiff without increasing the volume of build material deliverable byeach slat. Specifically, the slats can be shaped so that the momentcreated when they are dragged through the volume of build material tendsto wrap the conveyor chain onto a sprocket or a pulley. In addition, theslats can be shaped so that the moment created when the powder-carryingportion of the slat is dragged through the powder is cancelled by themoment created when the stiffener is dragged through the powder. Theconveyor system can be configured to deposit build material in front ofa spreader roller or a doctor blade, such as through alignment andorientation of the slats.

[0013] A metering system can be used regulate the quantity of buildmaterial deposited. In one embodiment, the conveyor system can be anaugur in a tube or pipes. The augur can then be rotatable to lift powderfrom the bottom of the feed reservoir to the metering system.

[0014] In another embodiment, the metering system can comprise acylinder inside a closely fitting tube. In this embodiment, the cylindercan have a cavity to hold a particular volume of build material and thetube can have a entrance slot and an exit slot. The cylinder can then berotatable inside the tube so that build material enters the cavity andis carried to the exit slot. More specifically, a clearance between thecylinder and tube is sized to restrict unwanted powder flow between theinlet slot and the outlet slot. Furthermore, a flicker blade can berotatable counter to the metering cylinder so that the flicker bladescrapes build material out of the cavity to prevent build material fromsticking therein.

[0015] In another embodiment, various mechanisms can be used to breakbridges and keep the build material flowing into the metering system.For example, a paddle wheel can be configured to agitate the buildmaterial above the metering system. As another example, a vibratingmember can be used to agitate the build material and can be coupled tothe chamber.

[0016] In accordance with another particular aspect of the invention, anembodiment of a three-dimensional printer can include a chamber forstoring build material above the plane of the build surface and ametering system. The metering system can be used to regulate thequantity of build material delivered by the feed reservoir.

[0017] In particular, the metering can comprise a cylinder inside aclosely fitting tube. In this embodiment, the cylinder can have a cavityto hold a particular volume of build material and the tube can have aentrance slot and an exit slot. The cylinder can then be rotatableinside the tube so that build material enters the cavity and is carriedto the exit slot. More specifically, a clearance between the cylinderand tube is sized to restrict unwanted powder flow between the inletslot and the outlet slot.

[0018] In another embodiment, various mechanisms can be used to breakbridges and keep the build material flowing into the metering system.For example, a paddle wheel can be configured to agitate the buildmaterial above the metering system. As another example, a vibratingmember can be used to agitate the build material and can be coupled tothe chamber.

[0019] The chamber and metering system can be mounted to a gantrycapable of moving across a build chamber. The powder can be metered ontothe build chamber to form a smooth layer. Specifically, the powder canbe metered in front of a roller or a doctor blade to create the smoothlayer.

[0020] Once the three-dimensional part is done being printed, it issurrounded by unbound powder. That unbound powder must be removed toreveal the printed object. Again, a technique is needed to mitigate thespread of the lose powder. Because most of the powder may be unbound,instead of bound as the part, there is an economic incentive to recyclethe unbound powder.

[0021] In accordance with another particular aspect of the invention, anembodiment of a three-dimensional printer includes an apparatus forremoving loose powder from the surface of a three-dimensional printedobject. A particular apparatus can include an enclosure for holding theobject, a blower for creating an airflow, at least one filter forremoving powder from the airflow, a system of ducts for channeling theairflow to the enclosure, and a tool for blowing compressed air onto theobject.

[0022] More particularly, the ducts can direct at least one portion ofthe exhaust of the blower down across the opening of the enclosure toprevent powder from being ejected from the booth. Furthermore, the ductscan direct at least a portion of the exhaust of the blower downwardthroughout the enclosure to eliminate stagnant air pockets and create ageneralized airflow from top to bottom of the enclosure. The airflow canbe divided between the air curtain and the generalized downward flow bydiverting the airflow through a duct in which there is very littlepressure drop.

[0023] In addition, the enclosure can be an integral part of the 3-Dprinter and the removal of loose powder occurs in the enclosure thathouses the 3-D printer. The apparatus can also include a back pulsecleaner to remove powder from the filter and a chamber for receiving theremoved powder. The powder removed from the filter can be automaticallyrecycled by an integral vacuum system.

[0024] Inkjet-type printheads are used to deliver binder to the layersof powder. Another problem with working with powder is that the powdertends to collect on the printheads. If the powder is left to accumulatefor a significant period of time, it can clog the jets. There istherefore a need to keep the printheads clean. There is also a need todetect faulty jets or printheads and to compensate for the failures.

[0025] In accordance with another particular aspect of the invention, anembodiment of a three-dimensional printer can include a structuralframe, a build chamber supported by the frame and suited to be filledwith a build material, a gantry mounted for displacement across thebuild chamber, a printhead mounted on the gantry, a printhead cleaningelement for cleaning the printhead, and a cleaning system for cleaningthe printhead cleaning element.

[0026] In particular, the cleaning system can include a supply of acleaning fluid and a mechanism for immersing the printhead cleaningelement into the cleaning fluid. To promote cleaning, the cleaning fluidcan be agitated by ultrasonic vibration or by circulating the cleaningfluid with a pump. Air can also be injected into the cleaning fluid toincrease the agitation.

[0027] Structurally, the printhead cleaning element can be mounted to amoveable belt. The cleaning system can also include a mechanism forwiping the printhead cleaning element across a stationary surface. Thestationary surface can be wetted with the cleaning fluid. The stationarysurface can be immersable in the cleaning fluid.

[0028] In accordance with another particular aspect of the invention, anembodiment of a three-dimensional printer can include a structuralframe, a build chamber supported by the frame and suited to be filledwith a build material, a gantry mounted for displacement across thebuild chamber, a printhead mounted on the gantry, and a printheadfailure detector for detecting if the printhead is functioning properly.

[0029] Various mechanisms can be used in the printhead failure detector.For example, the printhead failure detector can be an optical dropdetector. As another example, the printhead failure detector can includea membrane at which drops are fired by the printhead, where the dropscan be detectable by a microphone that detects the impact of the dropson the membrane. As yet another example, the printhead failure detectorcan include a piezo-electric element. Furthermore, in either case, theprinthead failure detector can detect the firing of individual jets ofthe printhead or a group of jets being fired simultaneously.

[0030] When the printhead is an array of more than one printhead, themode of operating the printer can be altered in response to a detectedfailure of a printhead. Specifically, the printing process can bechanged so that more than one pass is made over each area of the objectbeing printed. This can allow each area of the object to be printed bymore than one area of the array of printheads.

[0031] When the printhead is an array of 4 or more printheads, in whichat least one printhead is supplied with a binder containing a colorantfor each of the primaries, the mode of operating the printer can bealtered in response to a detected failure of a printhead. Specifically,printing can be changed from color to a multi-pass monochrome mode.

[0032] When the printhead is an array of more than one printhead, themode of operating the printer can be altered in response to a detectedfailure of a printhead on one end of the array. Specifically, theprinting process is changed so that the width of the printhead array isredefined.

[0033] After the part is removed from the mass of powder, it can bepost-processed. One step in the post-processing stage is infiltration.Infiltration involves applying a resin to the porous part. The resinsare typically adhesives that should be contained.

[0034] In accordance with another particular aspect of the invention, anembodiment of a three-dimensional printer can include an apparatus forinfiltrating a liquid into a three-dimensional printed part. Theinfiltration apparatus can include an enclosure for holding the part, afiltration system to remove infiltrant aerosols, and a sprayer forspraying infiltrant on the part.

[0035] In particular, the enclosure can be disposable. A filter elementcan also be incorporated into the disposable enclosure.

[0036] The filtration system can include a system for creating airflowthrough a filter element. The system for creating airflow can be a boothand the enclosure can be a disposable liner that prevents the booth frombecoming coated with infiltrant.

[0037] The sprayer can include a peristaltic pump, disposable tubing,and a disposable spray nozzle. The spray nozzle can create an aerosolspray of the infiltrant. The peristaltic pump can be a two-head pump andthe infiltrant can be a two-component material. The two components canbe mixed in a mixing chamber prior to entering the spray nozzle. Thecomponents can further be pumped through separate tubes, at the samerate by the pump. The two-component material, in particular, can have afixed mixing ratio and the inside diameters of the separate tubes can befixed in the same ratio so that the mixing ratio is maintained.

[0038] It should be understood that elements of the above embodimentscan be combined in various ways and are not exclusive to the describedembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The foregoing and other objects, features and advantages of theThree-Dimensional Printer will be apparent from the following moreparticular description of particular embodiments of the invention, asillustrated in the accompanying drawings in which like referencecharacters refer to the same parts throughout the different views. Thedrawings are not necessarily to scale, emphasis instead being placedupon illustrating the principles of the invention.

[0040]FIG. 1 is a schematic of a particular apparatus for rapidprototyping.

[0041]FIG. 2 is a perspective view of the 3-D printer assembly of FIG.1.

[0042]FIG. 3 is a perspective view of a particular powder feeder.

[0043]FIG. 4 is a perspective view of a powder loading subsystem.

[0044]FIG. 5 is a schematic of the 3-D printer assembly of FIG. 2 withseveral parts removed to reveal the overflow chamber.

[0045]FIG. 6 is a schematic of another embodiment of the overflowchamber of FIG. 5.

[0046]FIG. 7 is a schematic of a chunk separator.

[0047]FIG. 8 is a schematic of a filter system for the vacuum system ofFIG. 3.

[0048]FIG. 9 is a schematic of a powder delivery mechanism.

[0049]FIG. 10 is a more detailed view of a slat 123 at the drop point128.

[0050]FIG. 11 is a perspective view of an embodiment of a simple slat.

[0051]FIG. 12 is a perspective view of a particular embodiment of areinforced slat.

[0052]FIG. 13 is a schematic of a conveyor system of FIG. 9 thatdelivers powdered build material to a separate metering system.

[0053] FIGS. 14A-14B are schematics of the metering system of FIG. 13.

[0054]FIG. 15 is a schematic of an embodiment in which the feedreservoir 102 is entirely above the plane of the build surface 202 andintegrated into a printer unit 200.

[0055]FIG. 16A-16B are schematics of a particular cleaning station 300.

[0056]FIG. 17 is a schematic of another particular embodiment of acleaning station.

[0057]FIG. 18 is a schematic of a drop detector for monitoring thecondition of a printhead.

[0058]FIG. 19 is a schematic of a particular depowdering booth.

[0059]FIG. 20 is a schematic cutaway view of the depowdering booth ofFIG. 19.

[0060]FIG. 21 is a schematic of a particular diverter of FIG. 20.

[0061]FIG. 22 is a schematic of a depowdering booth incorporated intothe printer unit 200 of FIG. 15.

[0062]FIG. 23 is a schematic of a liner for the depowdering booth ofFIG. 19.

[0063]FIG. 24 is a schematic of a system for application of a resininfiltrant by spraying.

[0064]FIG. 25 is a schematic of a system for spraying a two-componentinfiltrant.

[0065]FIG. 26 is a front cross-sectional view of a sealed piston.

[0066]FIG. 27 is a schematic cross-section of a powder gutter.

[0067]FIG. 28 is a schematic cross-section of a magnetic plowconfiguration.

[0068]FIG. 29 is a schematic of a gravity-feed binder supply.

DETAILED DESCRIPTION

[0069]FIG. 1 is a schematic of a particular apparatus for rapidprototyping. As illustrated, there is a digital model 1, a computer 10,a three-dimensional (3-D) printer assembly 30, an as-printed (green) 3-Dphysical model 3, a post-processing system 50, and a completed 3-Dphysical model 5.

[0070] The digital model 1 is a data representation of an object to be3-D printed, that is, a digital object to be rendered into a tangiblephysical entity. Suitable digital models may be created using ComputerAided Design (CAD) software applications or 3-D scanning systems, bothof which are available from many different suppliers. The digital modelsare stored in industry-standard file formats, which can be transmittedelectronically and interpreted by application programs running onstandard computer equipment.

[0071] The computer 10 can be a personal computer, such as a desktopcomputer or a portable computer. The computer can be a stand-alonecomputer or a part of a network.

[0072] The computer 10 runs a custom software application program 15,which reads digital model files, accepts parameter and preference inputfrom the user, performs a series of detailed calculations and transmitsto the 3-D printer assembly 30 the information needed to fabricate thedesired physical model. In particular, the application program 15 allowsthe user to arrange one or more digital models in a virtual volumerepresenting the actual fabrication space within the 3-D printer 30. Theapplication program 15 then slices the array of digital models into aplurality of two-dimensional (2-D) layers, each of a predeterminedthickness, which are transmitted to an electronic control circuitry 32housed within the 3-D printer 30.

[0073] The 3-D printer 30 uses an array of ink jet type printheads 35 todeposit binder liquid 37 onto successive layers of a powdered buildmaterial 39, such as, disclosed in U.S. Pat. No. 5,902,441 to Bredt, etal., the teachings of which are incorporated herein by reference intheir entirety. Where the binder liquid 37 combines with the powderedbuild material 39, the powder reacts and hardens. By controlling theplacement of binder droplets from these printheads, the solid structureof the 2-D cross section can be physically reproduced. The 3-D printerfabricates a physical layer for each sectioned layer provided by theapplication program 15. When the complete set of 2-D cross sections hasbeen processed, a 3-D physical model 3 has been formed. The model atthis stage is termed “green” to indicate an as-printed condition, priorto post-processing. Further details of binding a powder to form anobject are disclosed in U.S. Pat. Nos. 5,340,656 to Sachs et al. and5,387,380 to Cima et al., the teachings of which are incorporated hereinby reference in their entirety.

[0074] The post-processing system 50 may be used to produce completedphysical models 5 by improving the appearance and the physicalproperties of green physical models 3. The post-processing system 50 mayoptionally a transport subsystem 52 for handling and transportingprinted models, a drying subsystem 54 for completely drying physicalmodels, a depowdering subsystem 56 for thoroughly removing the residualpowdered build material from printed models, and an infiltrationsubsystem 58 for coating and infiltrating printed models with varioussubstances.

[0075]FIG. 2 is a perspective view of the 3-D printer assembly ofFIG. 1. Its constituent subassemblies include a powder feeder 100 and aprinter unit 200. The powder feeder 100 and the printer 200 can beeasily uncoupled from each other for shipping, service and cleaning.Further, the user has the option of maintaining several interchangeablepowder feeders 100 for use with a single printer unit 200, each feedercontaining a different powdered build material to facilitate easychangeover from one material to another.

[0076] The following description describes particular features of the3-D printer assembly 30. The headings are meant as a guide to the readerand should not be considered limiting to the claimed invention.

Power Feeder

[0077]FIG. 3 is a perspective view of a particular powder feeder. Thepowder feeder 100 includes a vacuum subsystem 110 with an associatedvacuum inlet 112, a feed reservoir 102 storing a supply of the powderedbuild material 39 (FIG. 1), and a metering system 170, which deliverspowdered build material to the printer unit 200 in measured quantities.The following paragraphs describe in detail the design and operation ofthe powder feeder 100 and its subassemblies.

[0078] Vacuum System

[0079] Loading powder can be a messy process that can cause some of thepowder to become airborne and allow the powder to deposit on theprinter, the user, and the surrounding environment. Similar problemsexist with recycling powder that has not been printed upon. There aretwo types of recyclable powder: 1) powder that was deposited in thebuild chamber but that was not used to form a part; and 2) excess powderused for the spreading process in order to ensure a complete layer isdeposited; this excess powder ultimately drops into the overflowchamber. Both types of powder have the same difficulties in beingrecycled.

[0080]FIG. 4 is a perspective view of a powder loading subsystem. Thesubsystem loads the feed reservoir 102 with the powdered build material39. As in FIG. 3, a vacuum system 110 is attached to the feed reservoir102 (other embodiments could include a detached vacuum). The vacuumsystem 110 forms the top of the powder feeder 100. The feed reservoir102 is filled by drawing powdered build material from a shippingcontainer 9 into the feed reservoir through a vacuum hose 111 coupled tothe vacuum inlet 112. This allows the user to fill the reservoir withoutcontacting the powder.

[0081] Air can also be injected into the container 9 (which could be thecontainer in which the powder is shipped from its place of manufacture)through a compressed air hose 101. The compressed air aids in vacuumingthe powder out of the container by making the powder flow more easily.This technique can be automated so that the feed reservoir 102 maintainsa store of a sufficient quantity of build material.

[0082] A vacuum system having an outlet that empties into the feedreservoir of the 3-D printer, solves a variety of problems. By makingthe process cleaner, user satisfaction is increased and the machine ismade more reliable because less airborne powder, which can contaminatemachine components (e.g., bearing and electronics), is generated. Bymaking the process more convenient (less time and interaction isrequired by the user) user satisfaction and productivity are increased.

[0083] Once a physical model has been formed by the 3-D printingprocess, it is necessary to separate the model from the unprinted powder(described below). It is also desirable to reuse the unprinted powder.To those ends, the vacuum system 110 can be used to remove most of thepowder from the printed model 3 (FIG. 1).

[0084] Further, when the user has removed the model 3 from the printer,the user can use the vacuum system 110 to transport into the feedreservoir 102 the remainder of the powder in the build chamber and anypowder than has been deposited (by accident or design) elsewhere on theprinter. In particular, in the process of printing a physical model, the3-D printer 200 spreads successive layers of powdered build material inthe manner disclosed in U.S. Pat. No. 5,902,441 to Bredt, et al.,depositing a quantity averaging approximately 20% of total amount spreadinto an overflow chamber. Another specific use for the vacuum system 110is to return the powdered build material deposited in the overflowchamber to the feed reservoir 102.

[0085]FIG. 5 is a schematic of the 3-D printer assembly of FIG. 2 withseveral parts removed to reveal the overflow chamber 230. In theparticular embodiment shown in FIG. 5, the overflow chamber 230 isconnected through plumbing 113 and a valve 114 to the vacuum inlet 112.When the vacuum system 110 is activated, powdered build material fromthe overflow chamber 230 is drawn into the plumbing 113 and thence intothe feed reservoir 102. An opening 115 is provided at the valve 114 topermit a vacuum hose to be attached for performing the filling andcleaning functions described above. To use a vacuum hose connected tothe opening 115, the valve 114 is set to block the connection throughthe plumbing 113 to the overflow chamber 230 and open the connection tothe opening 115.

[0086]FIG. 6 is a schematic of another embodiment of the overflowchamber of FIG. 5. As shown, the overflow chamber 230 has an overflowchamber outlet 235 permanently attached at its lower end. To empty theoverflow chamber 230, the user attaches a vacuum hose at one end to theoverflow chamber outlet 235 and at the other end to the vacuum inlet 112of the vacuum system 110 (FIG. 3). The vacuum system 110 is thenactivated, and powdered build material is transported from the overflowchamber 230 to the feed reservoir 102.

[0087] If the inlet 112 of the vacuum system 110 is connected directlyto the feed reservoir 102, foreign matter may enter the feed reservoir.If the foreign matter is similar in particle size to the powdered buildmaterial (e.g., dust) the foreign matter may have no detectable effecton the 3-D printer or the 3-D printing process. If large particles orchunks enter the feed reservoir, however, these chunks may damage themechanism or, if they pass through the feed reservoir and are depositedin the build chamber, they may damage the physical model being printed.

[0088]FIG. 7 is a schematic of a chunk separator. As shown, the chunkseparator 120 is placed between the vacuum system inlet 112 and the feedreservoir 102. The separator 120 causes air, powdered build material andany entrained foreign matter that enters the inlet 112 to follow agenerally circular airflow path 122 around the inside of the device. Thepowdered build material and air pass upward through the separator screen125, leaving the separator 120, and entering the feed reservoir 102. Anyentrained foreign matter in the airflow 122 that is too large to passthrough the screen 125 continues to circulate around the interior of thedevice. This recirculation action tends to fracture and abrade anychunks of foreign matter, allowing some part of them eventually to passthrough the screen 125. A faceplate 127 of the separator 120 isremovable to provide an access port for removal of accumulated debris.

[0089]FIG. 8 is a schematic of a filter system for the vacuum system ofFIG. 3. As shown, the vacuum system 110 includes two filters 118-A,118-B located inside the feed reservoir 102 to prevent fine particles(such as the powdered build material) that are picked up by the vacuumsystem 110 from being exhausted to the room. One skilled in the art willrecognize that the filters will become coated with powdered buildmaterial, and that this coating will reduce the airflow through thefilter, reducing the pressure differential generated at the vacuum inlet112. The filter system is used to clean the filters.

[0090] A system of valves 119-A, 119B closes the vacuum source to asingle filter outlet and diverts air at or near atmospheric pressureinto the same outlet, reversing the flow direction and blowing offaccumulated powder, which then falls into the feed reservoir 102. Theother filter in the system maintains airflow and vacuum inside the feedreservoir 102 to induce this airflow. This purging cycle is periodicallysequenced through each filter element. In this manner the filters can becleaned without intervention by the user and without requiring the userto stop using the vacuum system while the filters are automaticallycleaned.

[0091] Powder Feeding

[0092] The principal function of powder feeder 100 is to deliverpowdered build material to the 3-D printer unit 200 in measuredquantities as required by the printing process.

[0093]FIG. 9 is a schematic of a powder delivery mechanism. The feedreservoir 102 has, in particular, volumetric capacity of approximately8.6 ft³, or enough powdered build material to print 1.75 of the largestphysical models possible within the constraints of the printer unit 200.The powder delivery mechanism 120 includes a conveyor 122 having slats123 attached to two strands of conveyor chain. The conveyor is driven byan electric motor and moves in recirculating fashion in the directionindicated by the arrows. The slats 123 pass through the powdered buildmaterial 39 in the feed reservoir 102, and each slat 123 carries some ofthe powdered build material 39 to a point above the plane of the buildsurface 202. As the slats 123 pass over a drive sprocket 125 they areinverted at drop point 128, and the powdered build material is dumpedonto the build surface 202 in position to be spread over the surface ofthe physical model being printed.

[0094]FIG. 10 is a more detailed view of a slat 123 at the drop point128.

[0095] The system shown in FIG. 9 has the added advantage that the slatsare constantly moving along the periphery of the feed reservoir 102. Inso doing, the motion of the slats 123 stirs the volume of powder andprevents bridges and areas of stagnant powder from being formed. It isdesirable to avoid stagnant areas because the powder in these areascannot be extracted from the feed reservoir by the conveyor system 122.Such stagnant areas represent powder that is wasted because it cannot beused during the normal operation of the feed conveyor.

[0096] For a reservoir with a large amount of powder, the force on theslats 123 being dragged through the reservoir by the conveyor 122 may bevery large. The slat geometry can be altered to stiffen themsufficiently to allow them to travel through the powdered build materialwithout permanently deforming.

[0097]FIG. 11 is a perspective view of an embodiment of a simple slat.The slat 123 includes a leg 124 and is connected to the two conveyorchains 122-A, 122-B. This slat delivers an optimum volume of powderedbuild material but may be too weak to withstand the loads placed uponit. The leg can be strengthened for greater stiffness.

[0098]FIG. 12 is a perspective view of a particular embodiment of areinforced slat. The same slat 123 includes an additional stiffeningmember 126 that adds to the strength of the member without increasingthe amount of powdered build material it delivers. The powder is carriedon the surface 123-S of the slat 123. This configuration has anadditional advantage that the moment created by the resistance of thepowder wraps the chain 122-A, 122-B onto its pulleys or sprockets. Amoment in the opposite direction tends to cause the chain to jam ratherthan going around the pulley or sprocket.

[0099] Powder Metering

[0100]FIG. 13 schematic of a conveyor system of FIG. 9 that deliverspowdered build material to a separate metering system. The meteringsystem 130 regulates the flow of powdered build material into the 3-Dprinter.

[0101] FIGS. 14A-14B are schematics of the metering system of FIG. 13.Referring to FIG. 14A, a cylindrical metering roller 133 is enclosed bya closely fitting tube 134. The metering roller 133 has four axialgrooves in its surface, which constitute metering cavities 135-A, 135-B,135-C, and 135-D. The tube 134 has an entrance slot 136 and an exit slot137. As the metering roller 133 rotates inside the tube 134, powderedbuild material enters a metering cavities 135-A through the entranceslot 136. As the metering roller 133 continues to rotate, powdered buildmaterial is captured between the metering roller 133 and the tube 134and is carried around to the exit slot 137, where it is discharged ontothe build surface 202 (FIG. 13).

[0102] The clearance between the metering roller 133 and the tube 134 isapproximately 0.015 in., which has been determined to be large enough toallow the metering roller 133 to rotate freely but small enough toprevent unwanted radial powder flow between the inlet slot 136 and theoutlet slot 137. The metering cavities 135 each hold approximately 3 in³of powdered build material, which is equal to the material required forthe smallest desirable increment of layer thickness. This allows anamount of powdered build material consistent with any desired layerthickness be delivered by causing the metering roller 133 to rotateuntil the appropriate number of metering cavities 135 have picked up anddelivered powdered build material.

[0103] Also shown is a paddle wheel agitator 138, which disturbs thepowdered build material above the metering roller 133 to break bridgesand keep the powdered build material flowing into the metering cavities135.

[0104] A flicker blade 139 rotates in the opposite direction from themetering roller 133. When a metering cavity 135 containing powderedbuild material enters the exit slot 137, the flicker blade 139 wipes thepowdered build material out of the metering cavity 135. This techniqueprevents variation in the amount of powdered build material delivered,even when the materials are sticky or have a tendency to bridge.

[0105]FIG. 15 is a schematic of an embodiment in which the feedreservoir 102 is entirely above the plane of the build surface 202 andintegrated into a printer unit 200′. Powder is metered out of the feedreservoir 102 onto the plane of the build surface 202 and spread over abuild box 220 by the gantry 210. The powder is then printed on by aprinthead or printhead array 205. In this embodiment the metering systemcould be located at the bottom of the feed reservoir and fed by gravity.In other embodiments, the metering system could be located at the bottomof the feed reservoir and the reservoir would include paddlewheel orvibratory mechanisms to ensure the flow of the powder into the meteringsystem if the powder is a type prone to clumping or bridging.

[0106] Although the powder can be delivered to one side of the buildchamber and then spread across the build chamber by a roller, the feedreservoir can be mounted to the gantry 210, which is capable of movingacross the build chamber. Powder could be continuously metered out ofthe feed reservoir and deposited directly onto the build chamber 220 asthe gantry is moved across. In one such embodiment, a roller or doctorblade could be used to smooth and level the surface after the feedreservoir passed over.

Printhead

[0107] Printhead Cleaning

[0108] The 3-D printer unit 200 uses an array of inkjet printheads toselectively dispense a binder material onto successive layers ofpowdered build material, selectively hardening the build material andforming 3-D physical models. This technology is disclosed in detail inthe incorporated patents, e.g., U.S. Pat. No. 5,902,441 to Bredt, et al.An aspect of a successful inkjet printing device is a technique forkeeping the face of the printhead clean. Keeping the printheads clean ina 3-D printing environment is particularly demanding because of the highconcentration of airborne powdered build material in the vicinity of theprinthead face. In most inkjet printers, the printhead face is routinelywiped with a squeegee-like wiper element.

[0109]FIG. 16A-16B are schematics of a particular cleaning station 300.As shown, a wiper element 305 is situated to wipe the face of aprinthead 205 as the printhead translates over the wiper 305 in the leftdirection indicated by the arrow. As the printhead 205 passes over thewiper element 305, contaminating material is transferred from the faceof the printhead 205 to the wiper element 305. This methods works wellas long as contaminating material is not allowed to accumulate on thewiper element.

[0110] As shown, the wiper element 305 is mounted on a belt 302. Thebelt 302 runs on pulleys 304-A, 304-B, which are rotatable by a motor306. The wiper element 305 is stationary in position to wipe the face ofthe printhead 205. As shown in FIG. 16B, the motor 306 has beenactivated, causing the wiper element 305 to be dragged over the cleaningsurface 308 of a wiper block 309 in the direction indicated by thearrow, transferring any accumulated contamination to the wiper block309. The wiper block 309 is routinely replaced to maintain a cleanwiping surface.

[0111]FIG. 17 is a schematic of another particular embodiment of acleaning station. In this cleaning station 300′, a wiper element 305′can be retracted for cleaning into the depressed cleaning station 300′,which is filled to a level 308′ with a cleaning fluid 309′. When thewiper element 305′ is retracted, it is fully immersed in the cleaningfluid 309′. An agitator 307 can agitate the fluid 309′ by various means,such as ultrasonic vibration, rapid circulation of the cleaning fluid,or injection of air bubbles.

[0112] Printhead Failure Detection

[0113] The service life of a printhead varies depending on use and othervariables that may not be controlled. Sometimes printheads failpartially, with some jets not firing while others continue to firenormally. At other times an entire printhead fails, with all of its jetsmalfunctioning. Because there is a large variation in how printheadsfail and in the overall life of a printhead and because the failure of aprinthead can cause the failure of the 3-D printer to produce thedesired physical model it is useful to be able to detect the conditionof a printhead and to be able to determine whether some, most or all ofits jets are firing.

[0114]FIG. 18 is a schematic of a drop detector for monitoring thecondition of a printhead. After the printhead 205 is moved into positionabove the drop detector 400, each jet of the printhead 205 is firedindependently a number of times sufficient for the detector topositively detect whether the jet is firing normally. In an alternativeembodiment, a group of jets is fired simultaneously, and the detectordetermines how many jets within each group are firing normally withoutdetermining which specific jets are malfunctioning. This method isquicker because several jets can be tested at once.

[0115] A particular drop detector 400 can work by optical means. Forexample, an emitter can emit a frequency of light to which the binder isopaque (infrared, for instance). That light beam is interrupted when adrop fired by the printhead passes through the beam. Failure to detectthe interruption indicates a malfunctioning jet. If the detection beamwere sufficiently narrow, miss-aimed jets can also be detected.

[0116] Another particular drop detector 400 works by detecting dropimpacts on a membrane attached to a microphone or a piezo-electricdetector.

[0117] Printhead Failure Compensation Strategies

[0118] Being able to detect whether each printhead is functioningproperly allows the design of different modes of operation for the 3-Dprinter. In the simplest mode of operation the print job is interruptedas soon as a malfunction is detected. The user may have a brief periodto replace the faulty printhead or else the job is aborted.Alternatively, the print job can be aborted in any case. This would savetime and reduce the amount of powder consumed. Without a drop detector,if the printhead fails partially, or if one printhead in a printer withseveral printheads fails totally or partially, a large quantity ofpowder could be printed on even though the resulting part would not beuseful. By aborting the print job when a defect is detected the usersaves the expense of the binder and powder that would have been wastedif the defect were not detected.

[0119] In another mode of operation, if some jets are determined to benonfunctioning but others are still functioning (as, for instance, ifone printhead in a multi-printhead array fails), the printing process ischanged so that more than one pass is made over each area of the part.By advancing the x-axis, 1/n of the normal distance for each pass of theprintheads in the y-axis each area will be printed by n different jets.The volume of binder printed in each pass would be reduced to 1/n thenormal amount. N can be selected so that the weak areas of the part(which are printed by n−1 functioning jets) are still strong enough toprovide a satisfactory part.

[0120] In still another mode of operation, if a printhead at one end orthe other of a multi-printhead array fails the width of the array isredefined (as having n−1 printheads where n is the normal complement ofprintheads) and the print job could be completed.

[0121] In a color 3-D printer having 4 or more printheads where at leastone printhead is supplied with binder with a colorant of one of theprimaries (cyan, magenta, and yellow) another mode of operation ispossible. In particular, if the detector determines that one of theprintheads has failed the job is completed in a monochrome mode (or, toimprove speed, a mode which uses all colors except the color of thefaulty printhead) using the overlapping print mode mentioned above. Inthis way the user can get a useful part but not a color part or, in thealternative case, a part that has color but is not colorized per thedesign.

Post Processing

[0122] Depowdering

[0123] Once a physical model has been printed and most of the unprintedpowdered build material has been removed, for example by using thevacuum system 110 shown in FIG. 3, it is desirable to now remove theremainder of the unprinted powdered build material. Because of adhesionbetween the unprinted powdered build material and the printed physicalmodel, it is usually not possible to remove all of the unprintedpowdered build material by using the vacuum system 110 alone. Thebalance of the powdered build material can be brushed away, but this canbe tedious or impossible for certain geometries and may damage adelicate physical model. A particular method for removing the loosepowdered build material from a physical model is to blow it off withcompressed air. However, this creates a number of problems by creatingan airborne cloud of powdered build material.

[0124]FIG. 19 is a schematic of a particular depowdering booth. A flowof air is created in the depowdering booth 500 to contain and direct thecloud of powdered build material created by a jet of compressed airdirected at a physical model. An aperture 503 provides access to theinterior of the depowdering booth 500. The physical model to bedepowdered rests on a surface 504 inside of the aperture 503. A window505, can be closed to help contain airborne powdered build material, andcan be opened to allow a large physical model to be placed within thedepowdering booth 500. A shroud 506 covers a blower 510 to attenuate thenoise generated by operation of the equipment.

[0125]FIG. 20 is a schematic cutaway view of the depowdering booth ofFIG. 18. Air is circulated through the depowdering booth 500 by theblower 510, which is powered by an electric motor 515. As indicated byarrows, air exits from the blower 510 into a diverter 530, where theflow is divided into two separate streams, a primary air curtain flow517 carried by an air curtain duct 518, and a secondary powder clearingflow 519. Both flows recombine in the vicinity of the physical model-3supported on a turntable 520, entraining powdered build material. Theflow then passes through openings in a supporting surface 522 andthrough filters 524. Filtered air exits from the filters 524 into aclean air plenum 526 and thence enters the inlet of the blower 510 tocomplete its circuit.

[0126] As air carrying powdered build material passes through thefilters 524, powdered build material collects on the surfaces of thefilters 524, eventually restricting the airflow and reducing theefficiency of the system. To maintain the filters 524 in an unobstructedstate, a pulse of air is periodically introduced into the interior ofthe filters 524 from the clean air plenum 526. This causes the flow ofair through the filters 524 to reverse momentarily, forcing theaccumulated powdered build material to separate from the surfaces of thefilters 524 and to fall into a drawer 528. The powder collection drawer528 can be removed to be emptied.

[0127] One objective is to prevent airborne powdered build material fromescaping from the aperture 503 of the depowdering booth 500 (FIG. 19),thereby contaminating the surrounding environment. In particular, when ahigh-speed jet of compressed air is directed at the physical model 3, asubstantial portion of the compressed air reflected from the physicalmodel may be directed out of the depowdering booth 500 toward the user.To prevent the escape of this airborne powdered build material, theprimary air curtain flow 517 (FIG. 20) is directed vertically down theface of the window 505 (FIG. 19), effectively capturing and deflectingthe outwardly directed stream.

[0128] If all of the blower exhaust were channeled to flow along theface of the booth 500, a very effective air curtain could be created. Inthat case, however, most of the air in the booth would be stagnant and aregion of slowly rotating air would be formed in the interior of thedepowdering booth 500. When powdered build material is blown off thephysical model 3, the slowly rotating air would quickly become opaquedue to the powder particles suspended in it. This opaque powder cloudwould be slow to dissipate, and would reduce the user's productivity.The secondary powder clearing flow 519, shown in FIG. 20, addresses thisproblem, creating a general downward flow throughout the booth so thatnone of the air is stagnant, and any powder cloud that develops willdissipate quickly.

[0129] The optimum balance between the primary air curtain flow 517 andthe secondary air clearing flow 519 varies somewhat with thecharacteristics of the powdered build material being removed and withthe geometry of the physical model being depowdered. For this reason,the diverter 530 is adjustable.

[0130]FIG. 21 is a schematic of a particular diverter of FIG. 20. Usinga user operated lever 532, a mechanical linkage 533 causes a divertervane 534 to rotate up and down as indicated by arrows around a pivotpoint 535. As the edge 536 of the diverter vane 534 moves downward, theprimary air curtain flow 517 down the air curtain duct 518 assumes moreof the total airflow. As the edge 536 of the diverter vane 534 movesupward, the secondary air cleaning flow 519 into the exhaust plenum 538assumes more of the total airflow.

[0131]FIG. 22 is a schematic of a depowdering booth incorporated intothe printer unit 200′ of FIG. 15. As shown, a blower 510 is coupled tothe depowdering booth 500. Air flows downward across the front openingof the booth 500, entrains powder, passes through filters (not shown)and is returned to the inlet of the blower 510. In this configuration,depowdering can be performed on the same equipment as printing

[0132] If the depowdering booth 500 is separate from the printer unit200′, a cart can be used to transfer large or heavy physical models tothe depowdering booth 500. Physical models are printed on a pallet,which is placed on the 3-D printer build table before printing begins.When printing is complete, the cart is positioned adjacent to theprinter unit 200′ and the gap between them is bridged by a set oftransfer rails. These rails carry a multiplicity of rollers, which allowthe pallet, carrying the printed physical model to slide smoothly ontothe cart. The cart is then positioned adjacent to the depowdering booth500, and transfer rails are used to slide the pallet, carrying theprinted physical model into the depowdering booth 500.

[0133] Infiltration

[0134] The physical models created by the 3-D printing process areporous, making it possible to change their properties by infiltratingthem with various resins. Resin can be applied to the physical model inmany ways including immersion, brushing and pouring. Each of thesemethods is time consuming, wasteful of resin or both. The presentinvention applies resin to the physical model by a spraying process.Many of the infiltrants used on 3-D printed models are adhesives.Spraying adhesives creates a number of problems. First, it is necessaryto contain any vapors created during the process (as for instance fromoverspray, or bounce back of atomized spray). If the vapors are notcontained they may deposit on the user, the user's clothing, or otherobjects. For certain infiltrants the vapors may pose a health orenvironmental hazard. Another problem with spraying adhesives is thatthe spray equipment gets coated with the adhesive and must be cleanedthoroughly after each use. This is tedious and may create health orenvironmental problems if the solvent for the adhesive is hazardous.

[0135]FIG. 23 is a schematic of a liner for the depowdering booth ofFIG. 19. A liner 560 protects the booth 500 from infiltrant overspray.The liner 560 includes a pre-filter 562 to capture airborne adhesivedroplets to prevent them from coating the filters 524 (FIG. 20) in thedepowdering booth 500. When a physical model has been depowdered in thedepowdering booth 500, the user unfolds the liner 560, which ispreferably made of corrugated cardboard, inside the depowdering booth560, and sprays infiltrant on the physical model. Alternatively, theliner can be used to protect a vent hood or ductless fume hood.

[0136]FIG. 24 is a schematic of a system for application of a resininfiltrant by spraying. In the system 600, resin is pumped throughdisposable tubing 604 from a infiltrant reservoir 602 by a peristalticpump 603, and is then forced through a disposable spray nozzle 605. Byusing a system of disposable components and a peristaltic pump, which isnot wetted by the adhesive, an inexpensive and user-friendly system forspraying adhesives is created. The clean up consists of disposing of thetubing and spray nozzle.

[0137]FIG. 25 is a schematic of a system for spraying a two-componentinfiltrant. A two-component infiltrant is an infiltrant that cures whenthe two components are combined. In the system 610, resin components arepumped through the disposable tubing 614 from infiltrant reservoirs 616,617 by a 2-head peristaltic pump 618. The two resin components arecombined in a static mixer 619 and the mixture is then forced through adisposable spray nozzle 615. The mixing ratio for the two-componentsystem can be maintained by using an appropriate diameter for each tube.In particular, a one to one ratio for the components requires that bothtubes be the same diameter.

Power Control

[0138] Piston Seal

[0139] It is important to seal the build and feed pistons so that loosepowder does not leak out through the sides and fall down below themachine, which can cause unwanted mess and potentially hurt themechanisms below.

[0140]FIG. 26 is a front cross-sectional view of a scaled piston. Asshown, an energized tube 712 pushes outward onto the felt 714 on theinner surface of a piston box 710. The tube 712 is enveloped by thepiston assembly plate 715 of the piston assembly 718 on its top andside. Felt 714 is placed in between the tube seal 712 and the side ofthe piston box 710 to form a seal.

[0141] Powder Gutter

[0142] 3-D printing involves a supply box, from which powder is fed, anda build box where part fabrication takes place. During the 3-D printingprocess, powder collects around these powder boxes on a surface (calledthe deck) until the powder can be vacuumed away. Powder that migratesduring the printing process can be a nuisance and can cause performanceproblems with parts of the 3-D printer, in particular the printhead andthe service station. For functional reasons, the printhead and theservice station must be located close to the plane of the top edges ofthe powder boxes. If the deck is coplanar with these top edges, anypowder that accumulates on the deck is potentially close to thesesensitive components. Therefore, a more desirable embodiment has thesurface of the deck depressed below the edges of the powder boxes,forming a gutter for the powder to fall into.

[0143]FIG. 27 is a schematic cross-section of a powder box. The printerdeck 802 is depressed below the top edges 804 _(T) of the powder boxes.This configuration forms a gutter 805 where the migrated powder cancollect.

[0144] Plows

[0145] Plows can prevent migrating powder from flowing off the sides ofthe piston boxes. One method is to use plows that are fastened to thegantry with springs, causing the plows to exert a force downward ontothe top deck of the 3-D printer. A particular printer includes a plowwith a small magnet inside to exert a force. This is easier to assembleand disassemble than the plow with a spring. A further improvementinvolves the location of the plows.

[0146]FIG. 28 is a schematic cross-section of a magnetic plowconfiguration. Plows 810-1 and 810-2 are affixed to the printer gantry210′ in such a way that they are free to move perpendicular to the walls804-1 and 804-2 of the powder boxes but are effectively fixed withrespect to the gantry 210′ in all other dimensions. Walls 804-1 and804-2 are constructed of a soft magnetic material such as steel. Eachplow has an embedded magnet 810-1 and 810-2 that acts upon itsrespective wall with enough force to keep the plow in tight contact withthe wall, forming a barrier to prevent powder 39 from spilling onto deck802 during a powder spreading operation.

Binder Supply

[0147] Gravity Feed Binder Supply

[0148] 3-D printing typically utilizes commercially available printheadsthat were designed for 2-D printing. A special binder material thatmatches the powder being printed is substituted for the ink normallydispensed by the printhead. Since a typical 3-D printed part requiresmuch more binder than can be contained inside a printhead, and sinceprintheads cannot practically be replaced while a part is being built,it is necessary to continuously replenish the binder in the printheadwhile the printer is operating. This is typically accomplished by makinga tubing connection between the moving printhead and a stationary supplyof binder.

[0149] For a printhead to operate properly, the pressure inside the headat the entrance to the inkjet channels must be maintained at a smallnegative pressure, typically at a pressure between −3 and −6 inches ofwater. One prior art technique employs an ink supply whose free surfaceis maintained at a level approximately 4 inches below the printheadoutlet. Printheads are available with built-in pressure regulators thatmaintain the required negative internal pressure while the printheadfeed line pressure varies over a broad range of positive pressures. Ingeneral, enough pressure must be exerted on the binder at the supply endof the binder feed tubing to cause binder to flow through the tube at anadequate rate to keep the printhead full. The pressure required dependsprimarily on the restrictive characteristics of the feed tubing and therelative height of the supply with respect to the printhead. One priorart technique employs a pump that maintains the supply pressure at theinlet to the printhead. Because of its complexity, this solution isexpensive and potentially unreliable.

[0150]FIG. 29 is a schematic of a gravity feed binder supply. As shown,a stationary supply of binder 1002 is plumbed to printhead 205 through alength of tubing 1004. The binder supply 1002 is located at a sufficientheight above the printhead 205 to keep the printhead supplied throughtubing 1004. In particular, the free surface of the binder may varybetween 3.5 and 5 inches above the bottom surface of the printhead. Thisheight provides enough pressure to supply the printhead with binder at arate in excess of the required 8 grams/minute through a segment oftubing having an inside diameter of {fraction (1/16)} inch and a lengthof approximately 6 feet. Persons skilled in the art will recognize thatother combinations of supply height and tubing dimensions could beselected to yield the required flow rate.

[0151] While this three-dimensional printer has been particularly shownand described with references to particular embodiments, it will beunderstood by those skilled in the art that various changes in form anddetails may be made without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. An apparatus for fabricating a three-dimensionalobject, comprising: a feed reservoir for storing a supply of buildmaterial usable to fabricate the object; a vacuum system having a vacuuminlet plumbed to the feed reservoir; a build chamber for receivingincremental layers of the build material from the feed reservoir; and anoverflow cavity for receiving an excess quantity of build materialtransferred from the feed reservoir but not received by the buildchamber.
 2. The apparatus of claim 1 wherein the vacuum inlet is coupledto a source of build material, the vacuum system transferring buildmaterial from the source of build material to the feed reservoir throughthe vacuum inlet.
 3. The apparatus of claim 2 wherein the source ofbuild material is at least one of a container of build material, thebuild chamber, the overflow cavity, or an area proximate to the feedreservoir or the build chamber.
 4. The apparatus of claim 3 wherein thesource of build material includes the overflow cavity and the buildmaterial is automatically transferred from the overflow cavity to thefeed reservoir.
 5. The apparatus of claim 3 wherein the source of buildmaterial includes the container, and further comprising a mechanism forinjecting air into the container.
 6. The apparatus of claim 1 whereinthe vacuum system comprises a particle filter for filtering particlesfrom the build material.
 7. The apparatus of claim 1 further comprising:at least one filter disposed within the vacuum system; and a cleaningmechanism to clean the at least one filter.
 8. The apparatus of claim 7wherein there are a plurality of filters, the cleaning mechanismincluding a valve system to direct a reversed airflow sequentiallythrough each of the filters to remove accumulated particles.
 9. Theapparatus of claim 8 wherein at least one filter maintains airflow andvacuum inside the vacuum.
 10. An apparatus for a three-dimensionalprinter comprising: a storage chamber for storing build material; and aconveyor for moving build material from the storage chamber to anoperating position.
 11. The apparatus of claim 10 wherein the conveyorstirs the build material in the storage chamber to inhibit the formationof bridges of build material and stagnant areas.
 12. The apparatus ofclaim 10 wherein the conveyor comprises a plurality of slats attached totwo strands of a conveyor chain, each slat carrying a quantity of buildmaterial.
 13. The apparatus of claim 12 wherein each slat deposits buildmaterial in front of a spreader roller, a doctor blade, or a meteringsystem.
 14. The apparatus of claim 12 wherein the slats are shaped sothat the moment created when they are dragged through the volume ofbuild material tends to wrap the conveyor chain onto a sprocket or apulley.
 15. The apparatus of claim 12 wherein the slats are shaped sothat the moment created when a carrying portion of the slat is draggedthrough the build material is cancelled by the moment created when astiffener is dragged through the build material.
 16. The apparatus ofclaim 10 further comprising a metering system to regulate the quantityof build material delivered to the operating position.
 17. The apparatusof claim 16 wherein the conveyor system includes an augur, the augurbeing rotatable to lift build material from the feed reservoir to themetering system.
 18. The apparatus of claim 16 wherein the meteringsystem comprises a cylinder inside a closely fitting tube, the cylinderhaving a cavity to hold a particular volume of build material, the tubehaving a entrance slot and an exit slot, the cylinder being rotatableinside the tube so that build material enters the cavity and is carriedto the exit slot.
 19. The apparatus of claim 18 further comprising aflicker blade rotatable relative to the cylinder so that the flickerblade scrapes build material out of the cavity to prevent build materialfrom sticking therein.
 20. The apparatus of claim 16 further comprisinga mechanism to break bridges to assist the flow of the build materialinto the metering system.
 21. The apparatus of claim 20 wherein themechanism to break bridges comprises a paddle wheel or a vibratingmember.
 22. The apparatus of claim 16 wherein the metering systemincludes a screw or chain moveable in a tube.
 23. The apparatus of claim10 further comprising a variable speed roller in communication with theoperating position, the roller speed being dependent on the propertiesof the build material
 24. The apparatus of claim 23 wherein the rollerspeed is variable along a slow axis to promote a smooth density of buildmaterial.
 25. An apparatus for a three-dimensional printer comprising: astorage chamber for storing build material; and a metering system toregulate the quantity of build material delivered from the storagechamber to an operating position.
 26. The apparatus of claim 25 whereinthe metering system comprises a cylinder having a plurality of groovesinside a closely fitting tube, the cylinder having a cavity to hold aparticular volume of build material, the tube having an entrance slotand an exit slot, the cylinder being rotatable inside the tube so thatbuild material enters the cavity and is carried to the exit slot. 27.The apparatus of claim 25 further comprising a mechanism to breakbridges and keep the build material flowing into the metering system.28. The apparatus of claim 27 wherein the mechanism to break bridgesincludes a paddle wheel or a vibrating member. 29 The apparatus of claim25 wherein at least a portion of the storage chamber and the meteringsystem are mounted to a gantry capable of moving to the operatingposition.
 30. The apparatus of claim 29 wherein the operating positionis in front of a roller or a doctor blade to form a smooth layer
 31. Anapparatus for removing loose powder from the surface of athree-dimensional printed object, comprising: an enclosure for holdingthe object; a blower for creating an airflow; at least one filter forremoving powder from the airflow; a system of ducts for channeling theairflow to the enclosure; and a tool coupled to the ducts for blowingcompressed air onto the object.
 32. The apparatus of claim 31 whereinthe ducts direct at least one portion of the exhaust of the bloweracross the opening of the enclosure to form an air curtain inhibitingpowder from being ejected from the booth.
 33. The apparatus of claim 32wherein the ducts direct at least a portion of the exhaust of the blowerthroughout the enclosure to inhibit stagnant air pockets and create ageneralized airflow within the enclosure.
 34. The apparatus of claim 31wherein the enclosure includes a build chamber for fabricating theobject.
 35. The apparatus of claim 31 further comprising a back pulsecleaner to remove powder from the filter and a chamber for receiving theremoved powder.
 36. The apparatus of claim 35 wherein the powder removedfrom the filter is automatically recycled by a vacuum system.
 37. Theapparatus of claim 31 further comprising a powder gutter.
 38. Theapparatus of claim 37 further comprising a moveable plow member incommunication with the powder gutter.
 39. An apparatus for infiltratinga liquid into a three-dimensional printed part comprising: an enclosurefor holding the part; a filtration system to remove infiltrant aerosols;and a sprayer for spraying infiltrant on the part.
 40. The apparatus ofclaim 39 wherein the enclosure is disposable.
 41. The apparatus of claim40 wherein the filtration system includes a filter element incorporatedinto the enclosure.
 42. The apparatus of claim 39 further comprising abooth for creating an airflow, and wherein the enclosure is a disposableliner for the booth that prevents the booth from becoming coated withinfiltrant.
 43. The apparatus of claim 39 wherein the sprayer includes:a peristaltic pump having at least one head; a disposable conduitcoupled to the peristaltic pump; and a disposable spray nozzle coupledto the conduit.
 44. The apparatus of claim 43 further comprising amixing chamber in which two components can be mixed prior to enteringthe spray nozzle, the two components being pumped through separate tubesby the peristaltic pump.
 45. The apparatus of claim 39 wherein the spraynozzle is a siphon nozzle that creates an aerosol spray of theinfiltrant.
 46. An apparatus for fabricating a three-dimensional objectcomprising a gravity-feed system for delivering a binder to a layer ofbuild material.
 47. An apparatus for fabricating a three-dimensionalobject, comprising: a feed reservoir for storing a supply of buildmaterial usable to fabricate the object; a vacuum system having a vacuuminlet plumbed to the feed reservoir; a build chamber for receivingincremental layers of the build material from the feed reservoir; aprinthead for depositing binder onto the incremental layers of the buildmaterial; a gravity-feed binder delivery mechanism for supply a quantityof binder to the printhead; an overflow cavity for receiving an excessquantity of build material transferred from the feed reservoir but notreceived by the build chamber; a conveyor for moving build material fromthe feed reservoir toward the build chamber; a metering system toregulate the quantity of build material delivered from the conveyor tothe build chamber; an enclosure for holding the object; and a sprayerfor spraying infiltrant on the object.
 48. The apparatus of claim 47further comprising: a blower for creating an airflow; at least onefilter for removing build material from the airflow; a system of ductsfor channeling the airflow to the enclosure; and a tool coupled to theducts for blowing compressed air onto the object;
 49. The apparatus ofclaim 47 further comprising a filtration system to remove infiltrantaerosols from the enclosure.
 50. A method of fabricating athree-dimensional object, comprising: in a feed reservoir, storing asupply of build material usable to fabricate the object; operating avacuum system having a vacuum inlet plumbed to the feed reservoir; in abuild chamber, receiving incremental layers of the build material fromthe feed reservoir; depositing binder onto the incremental layers of thebuild material via a printhead; supplying a quantity of binder to theprinthead with a gravity-feed delivery mechanism; in an overflow cavity,receiving an excess quantity of build material transferred from the feedreservoir but not received by the build chamber; moving build materialalong a conveyor from the feed reservoir toward the build chamber;regulating the quantity of build material delivered from the conveyor tothe build chamber via a metering system; holding the object in anenclosure; and spraying infiltrant on the object in the enclosure. 51.The method of claim 50 further comprising: creating an airflow with ablower; removing build material from the airflow with at least onefilter; channeling the airflow to the enclosure through a system ofducts; and blowing compressed air onto the object with a tool coupled tothe ducts;
 52. The method of claim 50 further comprising removinginfiltrant aerosols from the enclosure with a filtration system.
 53. Amethod of fabricating a three-dimensional object, comprising: in a feedreservoir, storing a supply of build material usable to fabricate theobject; operating a vacuum system having a vacuum inlet plumbed to thefeed reservoir; in a build chamber, receiving incremental layers of thebuild material from the feed reservoir; and in an overflow cavity,receiving an excess quantity of build material transferred from the feedreservoir but not received by the build chamber.
 54. The method of claim53 further comprising transferring build material from the source ofbuild material to the feed reservoir through the vacuum inlet.
 55. Themethod of claim 54 wherein the source of build material is at least oneof a container of build material, the build chamber; the overflowcavity, or an area proximate to the feed reservoir or the build chamber.56. The method of claim 55 automatically transferring build materialfrom the overflow cavity to the feed reservoir.
 57. The method of claim55 further comprising injecting air into the container of buildmaterial.
 58. The method of claim 53 further comprising filteringparticles from the build material with the vacuum system.
 59. The methodof claim 53 further comprising: disposing at least one filter within thevacuum system; and cleaning the at least one filter.
 60. The method ofclaim 61 wherein there are a plurality of filters, and cleaning includesoperating a valve system to direct a reversed airflow sequentiallythrough each of the filters to remove accumulated particles.
 61. Themethod of claim 60 further comprising maintaining airflow and vacuuminside the vacuum with at least one filter.
 62. A method of operating athree-dimensional printer, comprising: storing build material in astorage chamber; and moving build material along a conveyor from thestorage chamber to an operating position.
 63. The method of claim 62further comprising stirring the build material in the storage chamber toinhibit the formation of bridges of build material and stagnant areas.64. The method of claim 62 further comprising regulating the quantity ofbuild material delivered to the operating position via a meteringsystem.
 65. The method of claim 62 further comprising varying the speedof a roller in communication with the operating position, the rollerspeed being dependent on the properties of the build material
 66. Themethod of claim 65 wherein the roller speed is variable along a slowaxis to promote a smooth density of build material.
 67. A method ofoperating a three-dimensional printer, comprising: storing buildmaterial in a storage chamber; and regulating the quantity of buildmaterial delivered from the storage chamber to an operating position viaa metering system.
 68. The method of claim 67 further comprisingbreaking bridges to assist the flow of the build material into themetering system.
 69. The method of claim 67 wherein the operatingposition is in front of a roller or a doctor blade to form a smoothlayer
 70. A method of removing loose powder from the surface of athree-dimensional printed object, comprising: holding the object in anenclosure; creating an airflow; removing powder from the airflow with atleast one filter; channeling the airflow to the enclosure through asystem of ducts; and operating a tool coupled to the ducts for blowingcompressed air onto the object.
 71. The method of claim 70 whereinchanneling comprises directing at least one portion of the exhaust ofthe blower across the opening of the enclosure to form an air curtaininhibiting powder from being ejected from the booth.
 72. The method ofclaim 71 wherein channeling comprises directing at least a portion ofthe exhaust of the blower throughout the enclosure to inhibit stagnantair pockets and create a generalized airflow within the enclosure.
 73. Amethod of infiltrating a liquid into a three-dimensional printed part,comprising: holding the parting in an enclosure; removing infiltrantaerosols with a filtration system; and spraying infiltrant on the partwith a sprayer.
 74. The method of claim 73 wherein spraying includes:pumping infiltrant with a peristaltic pump having at least one head. 75.The method of claim 74 further comprising mixing at least two componentsin a mixing and pumping the at least two components through separatetubes by the peristaltic pump.
 76. The method of claim 73 whereinspraying comprises creating an aerosol spray of the infiltrant.
 77. Amethod of fabricating a three-dimensional object, comprising deliveringa binder to a layer of build material through a gravity-feed deliverysystem.
 78. An apparatus for fabricating a three-dimensional object,comprising: a means for storing a supply of build material usable tofabricate the object; a means for operating a vacuum system having avacuum inlet plumbed to the storing means; a means for receivingincremental layers of the build material at a build chamber from thestoring means; and a means for receiving an excess quantity of buildmaterial transferred from the storing means but not received by thebuild chamber.
 79. An apparatus for operating a three-dimensionalprinter, comprising: a means for storing build material in a storagechamber; and a means for moving build material along a conveyor from thestorage chamber to an operating position.
 80. An apparatus for operatinga three-dimensional printer, comprising: a means for storing buildmaterial in a storage chamber; and a means for regulating the quantityof build material delivered from the storage chamber to an operatingposition via a metering system.
 81. An apparatus for removing loosepowder from the surface of a three-dimensional printed object,comprising: a means for holding the object in an enclosure; a means forcreating an airflow; a means for removing powder from the airflow withat least one filter; a means for channeling the airflow to the enclosurethrough a system of ducts; and a means for operating a tool coupled tothe ducts for blowing compressed air onto the object.
 82. An apparatusfor infiltrating a liquid into a three-dimensional printed part,comprising: a means for holding the parting in an enclosure; a means forremoving infiltrant aerosols with a filtration system; and a means forspraying infiltrant on the part with a sprayer.
 83. An apparatus forfabricating a three-dimensional object, comprising a means fordelivering a binder to a layer of build material through a gravity-feeddelivery system.